Cation Transport in Dog Red Cells

Studies have been made on the cation transport system of the dog red cell, a system of particular interest because it has been shown that there is a marked dependence of cation fluxes on the cell volume. We have found that a 10% decrease in cell volume causes a large increase in 1 hr uptake of ²⁴Na as well as a considerable inhibition of ⁴²K uptake. This effect cannot be produced by a difference in medium osmolality but rather requires the cell volume to change. Dog red cell uptake of ²⁴Na is not inhibited by iodoacetate. Phloretin inhibits ²⁴Na uptake and lactate production, and virtually abolishes the volume effect on Na uptake. These several observations may be accounted for in terms of a working hypothesis which presupposes a cation carrier complex which pumps K into and Na out of cells of normal volume. When the cells are shrunken the carrier specificity shifts to an external Na-specific mode and there is a large increase in ²⁴Na uptake, driven by the inwardly directed Na electrochemical potential gradient.